Document GB-A-2 008 938 describes such a fixing device, comprising two latches which are mounted on the base and each of which co-operates with two anchoring members mounted on the vehicle floor. In order to fix the seat to the vehicle floor, the operator must simultaneously position the seat on the anchoring members and displace the two latches into the released position against the action of the resilient means. This fixing device of the prior art is therefore awkward to operate.